Studying galaxy clusters with CFHT
Henk Hoekstra

Abstract: Clusters of galaxies can be used to probe the cosmology, but to do so we require large surveys with well determined selection functions and masses. CFHT with its wide field imaging capabilities has been leading this area of research with the Red-sequence Cluster Surveys and the CFHTLS. These surveys can satisfy the need for large samples, with well determined selection functions. However, the masses cannot be derived directly. Furtunately a multiwavelength study of a smaller sample of clusters can help overcome (most of) this problem. For instance, the Canadian Cluster Comparison Project (another Megacam project) aims to derive accurate weak lensing and X-ray masses for a sample of 50 massive clusters. We will review this projects and demonstrate the key role that CFHT plays in this area of research.